I. Field
The present disclosure relates generally to electronics circuits, and more specifically to switches.
II. Background
Switches are commonly used in various electronics circuits for various applications. For example, switches are widely used in mixed-signal integrated circuits to sample analog signals. Sampling switches may be implemented with various types of transistors such as metal oxide semiconductor field effect transistors (MOSFETs). A sampling MOSFET switch typically receives an analog signal at a source and a control signal at a gate, passes the analog signal if the switch is turned on by the control signal, and blocks the analog signal if the switch is turned off by the control signal.
The performance of a sampling switch may be characterized by an on impedance when the switch is turned on and an off impedance when the switch is turned off. Low-distortion sampling may be realized with a high off-impedance to on-impedance ratio in combination with moderate device parasitics. For a MOSFET switch, the on and off impedances are determined by the voltages of the analog signal at the source and the control signal at the gate of the switch. A particular change in voltage (e.g., more than 1 Volt) between the gate and source may be needed to achieve a high off/on impedance ratio with moderate device size for acceptable parasitics. However, as integrated circuit (IC) fabrication technology improves and transistor size shrinks, lower power supply voltage is often used to avoid oxide breakdown due to smaller transistor geometry. With the power supply voltages of modern scaled semiconductor technologies approaching 1 Volt, realization of high off/on impedance ratio for good sampling performance becomes more challenging.
There is therefore a need in the art for switches that can achieve good performance even with low power supply voltages.